Slideshow: Katy Perry at House of Blues Katy Perry brought her debut headlining tour, "Hello Katy" -- and her larger-than-life stage-prop cat, Katy Purry -- to Boston's House of Blues. Highlights: a pussy joke, a period joke, a watermelon with the word "penis" on it, and a bunch of other certified borscht-belt blue humor that left the pre-teens in the audience cackling, and their moms looking horrified . . . that is, when said MILFs weren't losing their shit to "Hot and Cold."

The other side of heavy Loving heavy rock is a two-step process. Step one is easy: you hear something heavier than you've ever heard before, and you realize, "This is my thing." Step two is a little trickier: you wonder, "What is 'heavy'?" If you can accept the idea that a certain set of limitations leads to ultimate heaviosity, then — kudos! — you are a metalhead.